Rhodium-platinum plating bath and process

ABSTRACT

An electrolyte and process for electrodepositing a low stress and mirror bright rhodium-platinum alloy. The electrolyte comprises an aqueous solution of rhodium sulfate, platinum as P salt and sulfamic acid.

United States Patent Martini 1 51 June 20, 1972 RHODIUM-PLATINUM PLATING BATH AND PROCESS [72] Inventor: Albert Michael Martini, Florham Park,

[73] Assignee: Sel-Rex Corporation, Nutley, NJ.

[22] Filed: May 25, 1971 [21 Appl. No.: 146,808

[52] US. Cl ..204/43 UNITED STATES PATENTS 2,984,604 5/1961 Duva et al ..204/47 3,515,651 6/1970 Ohkubo ..2o4/43 3,528,895 9/1970 Simonian ..204/47 x OTHER PUBLICATIONS Abner Brenner, Electrodeposition of Alloys," Vol. ll, pp. 544-545, (1963).

Primary Exdminer-G L. Kaplan AttomeySamuel Kriegel 57 ABSTRACT An electrolyte and process for electrodepositing a low stress and mirror bright rhodium-platinum alloy. The electrolyte comprises an aqueous solution of rhodium sulfate, platinum as P salt and sulfamic acid.

13 Claims, No Drawings RHODIUM-PLATINUM PLATING BATH AND PROCESS BACKGROUND OF THE INVENTION Electrodeposited rhodium is used for a decorative coating and as a contact base metal because of its extreme hardness and resistence to corrosion and to wear. Rhodium plating is particularly useful as a protective coating for silverware, hollow ware, jewelry and for electronic products. Such deposits, however, tend to be brittle, especially thick deposits.

Electrodeposited platinum has not been as popular as rhodium in the jewelry and decorative filed because its color is darker than rhodium or silver and it tends to darken further with time. There would be a great interest in the above areas for obtaining bright low stress deposits of rhodium, platinum or mutual alloys of the two.

It is an object of this invention to provide a novel rhodiumplatinum plating bath which produces brighter electrodeposits than can be obtained from a bath of either metal alone.

It a further object of this invention to provide a novel process for obtaining brighter rhodium-platinum electrodeposits.

It is a more specific object of this invention to provide a novel plating bath which produces a ductile, low stress, mirror bright rhodium-platinum deposit.

It is another object of this invention to obtain an electroplated article having a ductile, low stress, mirror bright rhodium-platinum deposit.

Other objects and advantages of this invention become apparant from the following description.

SUMMARY OF THE INVENTION DETAILED DESCRIPTION In practicing the present invention rhodium sulfate, platinum P salt, and sulfamic acid are generally mixed with sufficient water to obtain the following approximate concentrations:

Rhodium metal (as the sulfate) Platinum metal (as platinum P salt) Sulfamic acid 0.1 153/1 0.04- 24.0gll 20g/l-saturation concentration Preferably the rhodium metal concentration ranges from about 0.5 to 12 g/l, most preferably from about 2 to 10 g/l. Preferably, the platinum metal varies from about 0.07 to 12 g/l, most preferably from about 0.1 to 10 g/l. The sulfamic acid concentration preferably varies from 30 g/l to saturation concentration, most preferably from 50 to 100 g/l.

A high rhodium bath is used for electrodepositing a predominantly rhodium containing alloy. In this high rhodium bath, the rhodium metal concentration generally ranges from about 1 to 12 g/l, preferably from about 2 to 7 g/l; the platinum metal concentration varies from about 0.04 to 1.2 g/l, preferably from about 0.1 to 0.7 g/l; and the sulfamic acid concentration varies from about 30 g]! to saturation concentration, preferably 50 to 100 g/l. The rhodium concentrations for the high rhodium bath can be further broken down according to the thickness of the deposit desired. For deposits of up to about 2 microinches thickness it is preferred that the rhodium content of the bath be 1 to 2 g/l; for deposits of 2 to 10 microinches, the rhodium content preferably is 2 to g/l; and for deposits greater than microinches, the rhodium content preferably is 2 to 10 g/l. The platinum content for each range of thickness varies proportionately with the rhodium content.

A high platinum bath is used for electrodepositing a predominantly platinum containing alloy. In this high platinum bath, the platinum metal concentration varies from about 2 to 24 g/l, preferably from about 5 to 12 g/l; the rhodium metal concentration varies from about 0.10 to 5 gll, preferably from about 0.2 to 2 g/l; and the sulfamic acid concentration varies from about 30 to saturation, preferably from about 50 to g/l.

In all the above baths, the limits of current density can usually be improved by the addition of concentrated sulfuric acid generally up to about 100 ml/l of solution, preferably from 1 to 50 ml/l of solution.

The plating solution of this invention can be used to coat any substrate that is capable of receiving an electrodeposit, particularly such basis metals as copper, brass, nickel, mild steel, silver and the like. Because the acid bath of this invention might cause dissolution of the basis metal thereby contaminating the bath, it is preferred that the basis metal be protected, eg. by flash coating with palladium, palladium-gold, or preferably gold, so as to inhibit attack on the basis metal. In the case where the basis metal contains iron, it is preferred that the basis metal first be preplated with, for example, nickel, copper, or silver, prior to flash coating. The rhodiumplatinum alloy may be deposited from the plating bath, at a temperature of about 60 to 180 F., by passing a current at a current density of about 5 to 40 ASP through the bath to a cathode immersed therein. Preferably the current density is about 10 to 30 ASP and the temperature about 80 to F. The lower temperatures are generally used for flash deposits and the higher temperatures for heavier deposits and for high platinum deposits.

The deposit obtained using the high platinum bath contains from about 90 to 99 percent platinum, preferably from about 93 to 98 percent by weight. The high rhodium bath yields a low stress, predominantly rhodium containing deposit which is mirror bright, ductile, and contains from about 90 to 99.5 percent rhodium, preferably from about 93 to 99 percent rhodium, most preferably from about 96 to 98.5 percent rhodium by weight, and from about 0.5 to 10 percent platinum, preferably from about 1.0 to 7 percent platinum, most preferably from about 1.5 to 4.0 percent platinum by weight.

The deposits obtained by the process of this invention range from flash coatings, eg. 2 microinches, up to thick coatings of 200 microinches or more. Preferably this process is used to obtain low stress deposits of 50 to microinches.

The addition of trace quantities of lead to the high rhodium bath of this invention increases the life of the bath with respect to mirror bright deposits. Generally, up to 10 mg. of lead metal is added per liter of bath, preferably from 2 to 6 mg/liter. The lead is added as a water soluble salt, preferably as lead nitrate.

The high rhodium bath is particularly useful for the plating of coins, jewelry, hollow water, tableware, and the like, giving a mirror bright finish which greatly adds to their appearance. The high rhodium bath is especially useful for plating silver articles, preferably those containing greater than 90 weight percent silver, in that the deposit inhibits tarnishing of the silver, probably because of the non-porous nature of the deposit. In plating silver articles with the high rhodium bath, it is preferred that the article first be given a flash coating of gold.

The invention may be further illustrated by the following examples:

EXAMPLE 1 2gms (as the sulfate) 0.05 (as platinum P salt) SOgmt.

Sml. concentrated Test Panels age brass gold struck Mirrot' bright deposits are obtained at 15 to 20 ASF and 110 to 120 F without agitation.

With agitation at 15 to 20 ASF and 1 10 to 120 F, full bright deposits are obtained except for slight haze on higher current density edges of panels.

Platinum metal increased to 0.12 g/l resulting in mirror bright deposits with agitation, eliminating the slight haze at 15 ASP. Slight haze still occurs however, at 20 ASP on edges of test panel.

Test panel is plated to 100 microinches, with agitation, and analysis shows that deposit contains 2 to 5 percent Pt. and is low stress.

Various items are plated in the above baths, including nail Test panels: Bright nickel plated brass with gold strike. Plating results:

Test panels are plated mirror bright (15ASF) with a finish approaching the color of a highly buffed silver piece. 0.5 to 5 minutes. Thickness: Flash to microinches.

Other items plated mirror bright with the above bath are: nail clippers bright nickel gold flash coins (silver) palladium gold flash and gold flash candle labrum total area 2 square feet. bright nickel plated+ gold flash.

ltems plated with the above bath:

a. Brass watch bezels are plated at 118 to 122 F. and 20 ASP for 20 to 42 minutes. Mirror bright, silver colored deposits are obtained having thicknesses of 100 to 200 microinches.

b. 2 to 14K gold rings are plated at 115 F. and 20 ASF for 5 minutes, without agitation. Deposits obtained are 10 to 15 microinches and mirror bright, and have a silver color.

c. Test panel of nickel plated brass with gold flash is plated at 1 10 to 115 F. and ASF, with agitation for 10 minutes. Deposit is 50 to 70 microinches, mirror bright and low stress, and has a silver color.

LII

a. A test panel of nickel plated brass with gold strike is plated at to F. and 20ASF for 2 minutes without agitation. A 2 microinch mirror bright deposit is obtained having a silver color.

A test panel of nickel plated brass with gold strike is plated at to F. and 20 ASP for 17 minutes with agitation. A 100 microinch semi-mirror bright deposit is obtained.

1 claim: 1. An electroplating bath for depositing rhodium-platinum alloy therefrom comprising an aqueous solution of:

Rhodium metal (as the sulfate) 0.1 to lSg/l Platinum metal (as P salt) 0.04 to 24g/l Sulfamic acid 20g/l saturation concentration 2. The bath of claim 1 comprising an aqueous solution of:

Rhodium metal (as the sulfate) 0.5 to l2g/l Platinum metal (as P salt) 0.07 to l2g/l Sulfamic acid 30g/l saturation concentration 3. The bath of claim 2 additionally containing up to about 100 ml/l concentrated sulfuric acid per liter of solution.

4. An electroplating bath for depositing a predominantly rhodium containing alloy comprising an aqueous solution of:

Rhodium metal (as the sulfate) 1 to l2g/l Platinum metal (as P salt) 0.04 to 1.2g/l

Sulfamic acid 30 g/l saturation concentration 5. The bath of claim 4 comprising an aqueous solution of:

Rhodium metal (as the sulfate) 2 to 73/1 Platinum metal (as P salt) 0.1 to 0.7g/l

Sulfamic acid 30 g/l saturation concentration 6. The bath of claim 5 wherein the sulfamic acid concentration is 50 to 100 gll.

7. The bath of claim 6 additionally containing up to about 100 ml/l of concentrated sulfuric acid per liter of solution.

8. The bath of claim 6 which additionally contains trace amounts of lead in solution.

9. The bath of claim 5 additionally containing up to about 100 ml/] of concentrated sulfuric acid per liter of solution.

10. A process of electroplating rhodium-platinum alloy comprising electrodepositing the rhodium and platinum upon a basis metal from the aqueous bath of claim 1.

11. A process for electroplating a predominantly rhodium containing alloy comprising electrodepositing rhodium and platinum upon a basis metal from the bath of claim 4.

12. A process for electroplating a predominantly rhodium containing alloy comprising electrodepositing rhodium and platinum upon a basis metal from the bath of claim 5.

13. A process for electroplating a predominantly rhodium containing alloy comprising electrodepositing rhodium and platinum upon a basis metal from the bath of claim 8.

11. A process for electroplating a predominantly rhodium containing alloy comprising electrodepositing rhodium and 5 platium upon a basis metal from the bath of claim 4. 

2. The bath of claim 1 comprising an aqueous solution of: Rhodium metal (as the sulfate)0.5 to 12g/lPlatinum metal (as P salt)0.07 to 12g/lSulfamic acid30g/l - saturationconcentration
 3. The bath of claim 2 additionally containing up to about 100 ml/l concentrated sulfuric acid per liter of solution.
 4. An electroplating bath for depositing a predominantly rhodium containing alloy comprising an aqueous solution of: Rhodium metal (as the sulfate)1 to 12g/lPlatinum metal (as P salt)0.04 to 1.2g/lSulfamic acid30 g/l - saturationconcentration
 5. The bath of claim 4 comprising an aqueous solution of: Rhodium metal (as the sulfate)2 to 7g/lPlatinum metal (as P salt)0.1 to 0.7g/lSulfamic acid30 g/l - saturationconcentration
 6. The bath of claim 5 wherein the sulfamic acid concentration is 50 to 100 g/l.
 7. The bath of claim 6 additionally containing up to about 100 ml/l of concentrated sulfuric acid per liter of solution.
 8. The bath of claim 6 which additionally contains trace amounts of lead in solution.
 9. The bath of claim 5 additionally containing up to about 100 ml/l of concentrated sulfuric acid per liter of solution.
 10. A process of electroplating rhodium-platinum alloy comprising electrodepositing the rhodium and platinum upon a basis metal from the aqueous bath of claim
 1. 11. A process for electroplating a predominantly rhodium containing alloy comprising electrodepositing rhodium and platinum upon a basis metal from the bath of claim
 4. 12. A process for electroplating a predominantly rhodium containing alloy comprising electrodepositing rhodium and platinum upon a basis metal from the bath of claim
 5. 13. A process for electroplating a predominantly rhodium containing alloy comprising electrodepositing rhodium and platinum upon a basis metal from the bath of claim
 8. 